This invention relates to a rotary kiln for drying a slurry of organic waste or sewage sludge, and more particularly to a rotary kiln for drying a slurry or the like having high adhesion.
Generally, since the slurry or the like, if allowed to stand, becomes a cause of the public nuisance, it is subjected to incinerating treatment. Since, however, the slurry contains therein a large amount of water, the water content in the slurry is first removed by a drier and then incinerated by an incinerator. In order to heat the slurry positively and effectively, a usual kiln is provided with a rotary drum rotated while causing a heated gas to be passed therethrough. In this type of rotary kiln, the slurry is lifted by a large number of lifters provided on the inner wall of the rotary drum, to be released and dropped in accordance with the drum rotation, whereby the slurry is exposed to the heated gas to remove the water content in the slurry. Such rotary kiln, however, has the drawbacks that the slurry introduced into the rotary drum adheres to the inner wall of the rotary drum and to the lifters to be disabled from being effectively dried; and particularly in the inlet portion of the rotary drum the slurry adheres to the inner wall of this inlet portion to form a slurry layer, whereby the effective drying area of the rotary drum is reduced to decrease the drying efficiency. For this reason, in such usual dryer or usual rotary kiln, the rotary drum should necessarily be made large in length, resulting in large size and high cost. Further, the usual rotary kiln has the drawback after the drying treatment is performed, the slurry as adhered has to be forcibly removed through a manual operation.
Under these circumstances, there has been proposed a rotary kiln wherein loop chains are attached to the inner wall of the rotary drum in order to enhance the drying efficiency and perform an effective drying treatment. In such improved rotary kiln, the loop chains so act as to forcibly remove the slurry adhered to the inner wall of the rotary drum by applying a hammering force to this inner wall through dropping due to their own weights as well as by making sliding movements on or along the inner wall of the rotary drum. In the loop type rotary kiln, however, the rotary drum is vibrated due to the hammering effect of the loop chain upon the rotary drum, so that a mounting base for the rotary drum should have a vibration proof structure. As a result, the loop type rotary kiln becomes complicated in construction and high in manufacturing cost and, furthermore, intermittently produces noises. Further, this loop type rotary kiln has the drawback that where the loop chains are arranged with high density, they are inconveniently entangled with each other with the result that they fail to be attached in large number to render it difficult to remove the slurry sufficiently.